From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 83AE337F8CA for ; Thu, 3 Sep 2026 08:00:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788422430; cv=none; b=ta7zfUEvwlswN1GuvyYddf3x7NaYDzsUa1bApFDnLypKWNabhp+XINQSafha03s203lOZvw6eFk7oXOOz4ylQXYopdR2T45E+dm60udbmDACwF5KwXWh0cdeQXeXCgXrHTS1SWnl2iQ2Y1Dugtv5STrC8v1zKBVkd+2EESkopMw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788422430; c=relaxed/simple; bh=IiSD1Kd6l72CtXC372nsMHFluY1YeXG015CTqpig3DM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZHiDcVYjPI4MmdN5k/v4MKQKBffHMlUoLgAV3/a+OlCbBdI63qY1V7hbKfzJIKGUrqfx1bctNABHkI0FnsX1RB6Kdy4g2qlpj9Wjo08Uj1pJyAqUneZQuGcJtld5N+JDQw/QjEWhy2U28Wnqur9EGtIoeZWB38TVzvdek8YEkMc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=d7iRT08p; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="d7iRT08p" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 359B31F000E9; Thu, 3 Sep 2026 08:00:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788422429; bh=mH9xxi+NuX/7rAStj5yokYt3AaeJoJgJZjMceCTL2nE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=d7iRT08pKtrpl+FS8F9XGYWGb54fjKRbJt/wm7yMpEXiokgdrv23tgEn8Dje5lFxB Xpel97egrz56kjU20xZ4pk4d0TtaQ+G+af792PD36Zccz2MkZQ/aMYkK85gA3YsjAD BGRwxxvOg7bPL2QDe7W6+cmgR2QlNoOo1+y7Y32T1P4YxFCmmjVSh+Osfiu3ya0Vl3 cjLDlkcxY70ZVR01S80kC9kcUhQt9eQobn7vu5qjlq3+4kGVEXa+xf8vBHOSGTMJfu BaOO4k16B0EpfQpyBMrlzKbuzQYoQ1cUGKB4mtlyZNUKNNbue7QcTW9+WydcfQpqe7 hgEgZEcEaUr2g== Message-ID: <76dd87e0-cd34-4ce2-9586-d7ff019b1fb9@kernel.org> Date: Thu, 3 Sep 2026 10:00:22 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 13/26] mm: introduce freetype_t To: Yosry Ahmed , Brendan Jackman Cc: Brendan Jackman , Borislav Petkov , Dave Hansen , Peter Zijlstra , Andrew Morton , David Hildenbrand , Mike Rapoport , Wei Xu , Johannes Weiner , Zi Yan , Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, Sumit Garg , Will Deacon , rientjes@google.com, patrick.roy@linux.dev, "Itazuri, Takahiro" , Andy Lutomirski , David Kaplan , Thomas Gleixner , Patrick Bellasi , Reiji Watanabe , Sean Christopherson References: <20260726-page_alloc-unmapped-v3-0-6f5729aa9832@google.com> <20260726-page_alloc-unmapped-v3-13-6f5729aa9832@google.com> From: "Vlastimil Babka (SUSE)" Content-Language: en-US Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/18/26 02:35, Yosry Ahmed wrote: >> >> +static inline >> >> +struct list_head *free_area_list(struct free_area *area, freetype_t type) >> >> +{ >> >> + int idx = freetype_idx(type); >> >> + >> >> + VM_WARN_ON(idx < 0); >> >> + return &area->free_list[idx]; >> > >> > Should we return NULL here if idx < 0 instead of an out of bounds >> > access? >> >> TBH my descending order of preference is: >> >> 1. >> >> BUG_ON(idx < 0); >> return &area->free_list[idx]; >> >> 2. >> >> if (WARN_ON(idx < 0)) // OR VM_WARN_ON >> return NULL; >> return &area->free_list[idx]; >> >> 3. >> >> VM_WARN_ON(idx < 0); >> return &area->free_list[idx]; >> >> 4. >> >> return &area->free_list[idx]; >> >> But I suspect[0] Vlastimil (and Linus) would order it the exact opposite >> way. >> >> [0]: https://lore.kernel.org/all/bd36e972-8900-4476-a66b-4dc218b21a4d@kernel.org/ >> >> And I care more about making Vlastimil (and Linus) happy than this tiny >> detail of the code, so I'll defer to him. The current style is a >> compromise, but maybe it's just a compromise that makes nobody happy. > > I think I prefer #2 (regardless of whether it's WARN_ON() or > VM_WARN_ON()), let's see if anyone disagrees. #2 can't work with VM_WARN_ON as it returns void. Otherwise if it evaluated the cond with DEBUG_VM and hardcoded false otherwise, it would be ideal. I don't remember why it's not. Do the callers all handle NULL safely? In that case #2 has some merit (maybe with WARN_ON_ONCE()) otherwise #3